1. Field of the Invention
The present invention relates to a process for producing an intermetallic compound-based composite material. More particularly, the present invention relates to a process for producing an intermetallic compound-based composite material, which process requires neither pretreatment for forming an intermetallic compound nor high-temperature/high-pressure conditions for forming a composite material from the matrix (the intermetallic compound) and a reinforcing material.
2. Description of Related Art
Composite materials are a macroscopic mixture of a plurality of materials, in which the mechanical properties of individual materials act synergistically and thereby properties not achievable with each single material alone have been made possible. Composite materials can be obtained by combining different materials according to various methods, and a number of material combinations are possible depending upon the kinds of matrix and reinforcing material used, the intended application, the intended cost, etc.
Among composite materials, metal-based composite materials or intermetallic compound-based composite materials are composite materials obtained by reinforcing a matrix, i.e. a metal (e.g. Al, Ti, Ni or Nb) or an intermetallic compound (e.g. TiAl, Ti3Al, Al3Ti, NiAl, Ni3Al, Ni2Al3, Al3Ni, Nb3Al, Nb2Al or Al3Nb), with an inorganic material (e.g. a ceramic). These metal-based composite materials or intermetallic compound-based composite materials are lightweight and have a high strength and, therefore, find wide applications in space, aviation and other fields.
Generally, an intermetallic compound-based composite material has characteristic features that it is superior in the thermal characteristics, and abrasive resistance characteristics derived from the mechanical and physical characteristics of the matrix. Typically, intermetallic compound-based composites have a defect of being inferior in fracture toughness compared with a metal-based composite material. Furthermore, intermetallic compound-based composites have a lower coefficient of thermal expansion and a high stiffness.
For producing an intermetallic compound-based composite material, there has been known a process which includes first producing an intermetallic compound powder by mechanical alloying or the like and subjecting the intermetallic compound and a reinforcing material (e.g. a fiber and/or particles), to hot press (HP) or hot isostatic press (HIP) under high-temperature and high-pressure conditions. Also for producing a metal-based composite material, there can be mentioned a process requiring a high pressure, such as impregnation under pressure, melt forging or the like.
Conventional processes for producing an intermetallic compound-based composite material have the following problems. That is, in order to produce an intermetallic compound-based composite material of sufficient density, it is necessary to apply a high temperature and a high pressure by HP, HIP or the like to obtain a sintered intermetallic compound. Therefore, a pretreatment step for formation of the intermetallic compound is necessary and, moreover, there are limitations to the capability and size of the production apparatuses used, which make it very difficult to produce a composite material of large size or complicated shape. Further, near-net shaping is impossible and a machining treatment is necessary in the later step.
Furthermore, since there is required, as the pretreatment step, synthesis of an intermetallic compound by MA or the like, production steps are many and complicated.
Thus, in conventional processes for producing an intermetallic compound-based composite material, a number of steps are necessary and, moreover, a high temperature and a high pressure are employed; therefore, conventional processes are costly.
JP-B-2,609,376 and JP-A-9-227969 and the like propose a method for producing a composite material to produce in situ an aluminide intermetallic compound, and its oxides, especially alumina in a surface layer of a preform comprising metal oxides and the like being reducible with Al and the like by subjecting the preform to reaction with a liquefied Al and the like on said surface layer in order to the solve the above-mentioned problems.
However, in the case of the methods disclosed JP-B-2,609,376 and JP-A-9-227969, the design of the objective composite materials is restricted within the specific combination of the starting materials due the reinforcing materials to be dispersed in the objective composite material are restricted to the specific ones. Thus, it is difficult to modify the characteristic features of the composite materials by changing the combination of the starting materials. Furthermore, those methods have the problem in that metal oxides or the like, or Al or the like remains without reacting if the amounts of the starting materials are not strictly controlled. Moreover, it often becomes impossible to control the reaction since a large amount of the heat of the reaction is generated within instantly.
Incidentally, JP-B-3,107,563 discloses a method for producing a metal-based composite material which comprises forming a preform from fine particles of the reinforcing material and fine particles of Ti and the like having gettering effects of oxygen and nitrogen, and then immersing thus formed preform into Al melt and the like, thereby matrix made of Al and the like is formed.
However, in the case of the method disclosed in JP-B-3,107,563, the form of the produced composite material is restrictive due to the limitation of the production equipment since the preform should be retained in a metal melt to form the matrix therefrom for a predetermined period of time. Indeed, the composite materials producible are limited to a metal-based composite material in which a metal is used to form a matrix.